Preparation of naphthalocyanines

ABSTRACT

A process is described for preparing alkoxy-octasubstituted metal-free or metal-containing naphthalocyanines by etherification of 1,4-dihydroxy-2,3-dicyanonaphthalene and formation of the metal-free naphthalocyanine with or without subsequent metallization.

This application is a 317 of PCT/EP94/00863 Mar. 18, 1994.

The present invention relates to a novel process for preparingalkoxy-octasubstituted metal-free or metal-containing naphthalocyaninesby etherification of 1,4-dihydroxy-2,3-dicyanonaphthalene and formationof the metal-free naphthalocyanine with or without subsequentmetallization.

EP-A-433 220 describes the preparation of metal-free andmetal-containing naphthalocyanines starting from1,4-dihydroxy-2,3-dicyanonaphthalenes. Furthermore, GB-A-2 200 650discloses the preparation of these naphthalocyanines starting from1,4-dialkoxy-2,3-dicyanonaphthalenes. Finally, individual steps aredescribed in J. Org. Chem. 29 (1964), 3591, and in J. Chem. Soc., PerkinTrans. I (1988), 2453. However, it has been found that the prior artmethods give the naphthalocyanines only in unsatisfactory yield andpurity.

It is an object of the present invention to provide a novel process forpreparing naphthalocyanines, which can be carried out in a simple mannerand by means of which the target products can be obtained in high yieldand purity.

We have found that this object is achieved by a process for preparingnaphthalocyanines of the formula I ##STR1## where Me is twice hydrogenor a bivalent metal-containing radical with or without further ligands,and

R is in each case C₁ -C₂₀ -alkyl, which may be interrupted by from 1 to3 oxygen atoms in ether function, or C₄ -C₂₀ -alkenyl,

by etherification of 1,4-dihydroxy-2,3-dicyanonaphthalene and formationof the metal-free naphthalocyanine with or without subsequentmetallization, which comprises

a) in a first step reacting the 1,4-dihydroxy-2,3-dicyanonaphthalenewith an alkylating agent of the formula II

    R--X                                                       (II),

where X is bromine or the radical RO--SO₂ O and R is in each case asdefined above, in a molar ratio of from 1:2 to 1:3 in the presence of adiluent and of a base, pouring the reaction mixture onto water,filtering the precipitated dicyanonaphthalene of the formula III##STR2## where R is in each case as defined above, off with suction, andwashing and drying it,

b) in a second step converting the dicyanonaphthalene of the formula IIIwith an alkali metal alkoxide into the naphthalocyanine of the formula Iwhere Me is twice hydrogen in the presence of an alcohol, the molarratio of alkali metal alkoxide:dicyanonaphthalene. III being from 1:2.5to 2.5:1, and optionally then

c) in a third step converting the resulting metal-free naphthalocyanineby reaction with a metal salt in the presence of an alcohol into themetal-containing naphthalocyanine of the formula I where Me is ametal-containing ligand, the naphthalocyanine and the metal salt beingreacted with each other in a molar ratio of from 1:1 to 1:10.

All alkyl and alkenyl groups appearing in the abovementioned formulaemay be straight-chain or branched.

The radicals R can be identical or different.

R is for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl,sec-butyl, pentyl, isopentyl, neopentyl, tert-pentyl, hexyl,2-methylpentyl, heptyl, octyl, 2-ethylhexyl, isooctyl, nonyl, isononyl,decyl, isodecyl, undecyl, dodecyl, tridecyl, 3,5,5,7-tetramethylnonyl,isotridecyl (the above designations isooctyl, isononyl, isodecyl andisotridecyl are trivial names derived from the oxo process alcohols--cf.Ullmanns Encyklopadie der technischen Chemie, 4th Edition, Volume 7,pages 215 to 217, and also Volume 11, pages 435 and 436), tetradecyl,pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl,2-methoxyethyl, 2-ethoxyethyl, 2-propoxyethyl, 2-isopropoxyethyl,2-butoxyethyl, 2- or 3-methoxypropyl, 2- or 3-ethoxypropyl, 2- or3-propoxypropyl, 2- or 3-butoxypropyl, 2- or 4-methoxybutyl, 2- or4-ethoxybutyl, 2- or 4-propoxybutyl, 2- or 4-butoxybutyl,3,6-dioxaheptyl, 3,6-dioxaoctyl, 4,8-dioxanonyl, 3,7-dioxaoctyl,3,7-dioxanonyl, 4,7-dioxaoctyl, 4,7-dioxanonyl, 4,8-dioxadecyl,3,6,8-trioxadecyl, 3,6,9-trioxaundecyl, butenyl, but-3-en-1-yl,pentenyl, pent-4-en-1-yl, 3-methyl-but-3-en-1-yl, hexenyl, heptenyl,octenyl, nonenyl, decenyl, undecenyl, undec-10-en-1-yl, dodecenyl,tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl,octadecenyl, nonadecenyl or eicosenyl.

A suitable bivalent metal-containing radical is in particular copper.

Preference is given to a procedure for preparing naphthalocyanines ofthe formula I where Me is twice hydrogen or copper.

Preference is further given to a procedure for preparingnaphthalocyanines of the formula I where R is in each case C₂ -C₁₃-alkyl or C₄ -C₁₁ -alkenyl or in particular C₂ -C₈ -alkyl, attentionbeing drawn in particular to the preparation of those naphthalocyaninesof the formula I where R is in each case C₄ -alkyl or a C₂ /C₅ -alkylmixture.

In Step 1 of the process of the invention,1,4-dihydroxy-2,3-dicyanonaphthalene is reacted with an alkylating agentII in the presence of a diluent.

The molar ratio of 1,4-dihydroxy-2,3dicyanonaphthalene:alkylating agentII is from 1:2 to 1:3, preferably from 1:2.2 to 1:2.4.

As recited above, suitable alkylating agents are the correspondingbromine compounds (R--Br) or dialkyl sulfates (ROSO₂ OR), the dialkylsulfates being preferred in the case of lower alkyl (methyl or ethyl)while the bromine compounds are preferred for the other radicals.

The alkylating step is carried out in the presence of a diluent and of abase. Suitable diluents include for example N,N-dimethylformamide,N,N-diethylformamide, N-methylpyrrolidone and dimethyl sulfoxide. Theuse of N,N-dimethylformamide is preferred.

Suitable bases include for example alkali metal carbonates, such aslithium carbonate, sodium carbonate or potassium carbonate. The use ofpotassium carbonate is preferred.

The amount of base used is generally from 1.5 to 3 mol per mole of1,4-dihydroxy-2,3-dicyanonaphthalene. The amount of diluent used isgenerally from 400 to 700% by weight, based on the weight of1,4-dihydroxy-2,3-dicyanonaphthalene.

Step 1 of the process according to the invention is customarily carriedout at from 80° to 120° C.

It is generally carried out by introducing the1,4-dihydroxy-2,3-dicyanonaphthalene and the diluent as the initialcharge and adding the base and the alkylating agent II. However, it isalso possible to reverse this order and, for example, introduce the1,4-dihydroxy-2,3-dicyanonaphthalene, the diluent and the alkylatingagent II as the initial charge and add the base, or introduce the1,4-dihydroxy-2,3-dicyanonaphthalene, the diluent and the base as theinitial charge and add the alkylating agent II. The resulting mixture isthen kept at the abovementioned temperature for from 4 to 10 hours withstirring.

In the rest of the workup, the mixture is poured onto water and theprecipitated dicyanonaphthalene of the formula III is filtered off withsuction, washed and dried.

Without further purification it can be used directly in Step 2 of theprocess according to the invention, which method is preferred.

The preparation of the starting 1,4-dihydroxy-2,3-dicyanonaphthalene isdescribed for example in J. Org. Chem. 29 (1964), 3591.

In Step 2 of the process according to the invention, thedicyanonaphthalene of the formula III is converted into the metal-freenaphthalocyanine of the formula I by means of an alkali metal alkoxidein the presence of an alcohol.

The dicyanonaphthalene III and the alkali metal alkoxide are used in amolar ratio of from 1:2.5 to 2.5:1, preferably from 1:2 to 2:1.

Suitable alkali metal alkoxides include for example lithium, sodium orpotassium salts of methanol or ethanol. The use of the sodium orpotassium salts is preferred, the use of sodium methoxide or sodiumethoxide being particularly preferred. It is further of particularadvantage to add the alkali metal alkoxides in alcoholic solution.

Suitable alcohols include for example C₁ -C₂₀ -alkanols, whose alkylchain may be interrupted by from 1 to 3 oxygen atoms in ether function,such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol,sec-butanol, pentanol, isopentanol, neopentanol, tert-pentanol, hexanol,heptanol, octanol, isooctanol, 2-ethylhexanol, nonanol or decanol, or C₄-C₂₀ -alkenols, such as but-3-en-1-ol, pent-4-en-1-ol orundec-10-en-1-ol.

The use of C₂ -C₁₂ -alkanols or C₄ -C₁₁ -alkenols is preferred, with C₃-C₆ -alkanols being particularly preferred.

The alcohol is generally used in an amount of from 300 to 1000% byweight, based on the weight of dicyanonaphthalene of the formula III.

Step 2 of the process according to the invention is advantageouslycarried out by introducing the alkali metal alkoxide, the alcohol andthe dicyanonaphthalene III as the initial charge and heating saidinitial charge with stirring to 90°-160° C. with or without a protectivegas atmosphere, for example nitrogen or helium.

It is also possible to use as the initial charge a solution, for exampleof sodium methoxide in methanol, together with the alcohol and to heatthis mixture to distill off methanol. After the methanol has beenremoved, the dicyanonaphthalene III can be added.

The reaction generally takes from 0.25 to 6 hours. The alcohol can thenbe distilled off in full or in part (at least half being removed),methanol added to the residue, and the precipitated metal-freenaphthalocyanine of the formula I (Me=twice hydrogen) filtered off withsuction, washed with methanol and dried.

The metal-free naphthalocyanine is obtained in good purity and canwithout further purification be used directly further, for example forthe metallization reaction.

The resulting naphthalocyanine is found to have undergone atransalkylation (up to 100% ) of the R radicals in that, during theformation of the naphthalocyanine, all or some of the OR radicalspresent on the naphthalene ring are replaced by the alkoxide radicals ofthe alcohol used.

It is also possible to transalkylate the ready-formedoctaalkoxynaphthalocyanine. This can be done for example by treating theoctaalkoxynaphthalocyanine with sodium methoxide and an alcohol whosealkoxy moiety is different from the alkoxy groups present on thenaphthalocyanine.

The metal-free naphthalocyanine of the formula I is then optionallyconvertible in a third step into a metal-containing naphthalocyanine.For this it is reacted with a metal salt in the presence of an alcohol.The naphthalocyanine and the metal salt are used in a molar ratio offrom 1:1 to 1:10, preferably from 1:1 to 1:1.2.

Step 3 can also be carried out by using the as-obtained reaction mixtureof Step 2 directly, ie. without intermediate isolation of the metal-freenaphthalocyanine. This method is preferred.

The alcohol is generally used in an amount of from 1000 to 2000% byweight, based on the weight of metal-free naphthalocyanine I.

Suitable metal salts include for example copper salts, such ascopper(II) acetate, copper(I) chloride, copper(II) chloride, copper(II)sulfate and copper(II). acetylacetonate. The use of copper(II) acetateor copper(I) or copper(II) chloride is preferred.

Suitable alcohols for this step include for example propanol, butanol orpentanol.

When the metallization is carried out without intermediate isolation ofthe metal-free naphthalocyanine, an alcoholic reaction medium is alreadypresent. In this case the metallization can be carried out directly inthis medium or, if necessary, the medium can be additionally dilutedwith further alcohol.

In some cases it can also be of advantage to carry out the metallizationin the presence of bases, for example 1,4-diazabicyclo[2.2.21]octane or1,5-diazabicyclo[5.4.0]undec-5-ene.

Step 3 of the process according to the invention is advantageouslycarried out by heating a mixture of metal-free naphthalocyanine I, metalsalt and diluent with or without base to 80°-160° C. with stirring. Thereaction generally takes from 5 to 20 hours. After the reaction hasended, the diluent can be distilled off in full or in part (at leasthalf being removed). The residue can be admixed with petroleum ether andthe metal-containing naphthalocyanine filtered off with suction, washedand dried.

The process of the invention, which can be carried out continuously aswell as batchwise, is simple to practice and provides the targetproducts in high yield and purity, the yield and purity of the novelprocess being distinctly higher than in the abovementioned, prior artprocesses.

The metal-free or metal-containing naphthalocyanines of the formula Iare useful IR-absorbing compounds, which can be used for example inprinting inks (see for example EP-A-0 553 614).

The Examples which follow illustrate the invention.

I. Alkylation

EXAMPLE 1

42 g (0.2 mol) of 1,4-dihydroxy-2,3-dicyanonaphthalene and 200 ml ofN,N-dimethylformamide (DMF) were introduced at room temperature as theinitial charge. 55.4 g (0.44 mol) of dimethyl sulfate and 60.8 g (0.44mol) of potassium carbonate were added. The batch was slowly heated to100° C. and stirred at that temperature for 8 h. It was then poured ontowater, and the resulting precipitate was filtered off with suction,washed With water and dried to leave 30 g of1,4-dimethoxy-2,3-dicyanonaphthalene (theory: 64%; melting point: 190°C.).

EXAMPLE 2

21 g (0.1 mol) of 1,4-dihydroxy-2,3-dicyanonaphthalene, 100 ml ofdimethyl sulfoxide and 38.5 g (0.25 mol) of diethyl sulfate wereintroduced at room temperature as the initial charge. 38.6 g (0.28 mol)of potassium carbonate were added with stirring. The batch was thenstirred at 100° C. for 10 h and thereafter poured onto ice-water, andthe resulting precipitate was washed with water and dried to leave 23.3g of 1,4-diethoxy-2,3-dicyanonaphthalene (theory: 87%; melting point:167° C.).

EXAMPLE 3

210 g (1 mol) of 1,4-dihydroxy-2,3-dicyanonaphthalene, 1 l of DMF and339 g (2.2 mol) of diethyl sulfate were introduced at room temperatureas the initial charge. 304 g (2.2 mol) of potassium carbonate were addedwith care. The batch was gradually heated to 100° C. and stirred at 100°C. for 6 h. It was then poured onto water and the resulting precipitatewas washed with water and dried to leave 231 g of1,4-diethoxy-2,3-dicyanonaphthalene (theory: 87% ; melting point:167°-169° C.).

EXAMPLE 4

105 g of 1,4-dihydroxy-2,3-dicyanonaphthalene, 145 g of potassiumcarbonate and 500 ml of DMF were introduced as the initial charge. 155 gof 4-bromobutane were added. The batch was then heated to 100° C. withstirring and subsequently stirred at that temperature for 6 hours.Thereafter the reaction mixture was cooled down and poured into 2000 mlof ice-water. The precipitate was filtered off with suction, washed withwater and dried at 60° C. under reduced pressure to leave 120 g of1,4-dibutoxy-2,3-dicyanonaphthalene (theory: 90%; melting point: 69°-70°C.).

II. Naphthalocyanine formation

EXAMPLE 5

3 g (0.13 mol) of sodium were dissolved in 500 ml of ethanol, and 53.2 g(0.2 mol) of 1,4-diethoxy-2,3-dicyanonaphthalene were added. The batchwas then stirred under reflux for 4 h. Almost all the ethanol (about 450ml) was then distilled off under a water pump vacuum. Thereafter 600 mlof methanol were added to the reaction mixture and the reaction mixturewas then stirred at room temperature for 5 h. The precipitated productwas filtered off with suction, washed with methanol and dried to leave23 g of octaethoxynaphthalocyanine (theory: 43%; λ_(max) : 856 nm; ε:264 000 (in toluene)).

EXAMPLE 6

47 g (0.26 mol) of 30% strength by weight methanolic sodium methoxidesolution and 700 ml of n-propanol were introduced as the initial charge.The methanol was then distilled off under atmospheric pressure untiljust below the boiling point of propanol (97° C.). After cooling down,106 g (0.4 mol) of 1,4-diethoxy-2,3-dicyanonaphthalene were added undernitrogen and the batch was subsequently stirred under reflux for 3 h.The propanol was then distilled off under a water pump vacuum except forabout 50 ml, and 1 l of methanol was added. After stirring at roomtemperature for 8 h the precipitated product was filtered off withsuction, washed with methanol and dried to leave 61.8 g of anaphthalocyanine which according to N-NMR had been 75% transalkoxylated(R=75% propyl and 25% ethyl) (theory: 53%, λ_(max) : 858 nm; ε: 263 000(in toluene)).

EXAMPLE 7

25 ml of 30% strength by weight methanolic sodium methoxide solution and500 ml of butanol were introduced as the initial charge. The methanolwas distilled off under atmospheric pressure to just below the boilingpoint of butanol. (117.8° C.). After cooling down, 65 g of1,4-dibutoxy-2,3-dicyanonaphthalene were added under nitrogen and thebatch was subsequently stirred under reflux for 2 h. Then 350 ml ofbutanol were distilled off and 400 ml of methanol were added. Afterstirring at room temperature for 12 h the precipitated product wasfiltered off with suction, washed with methanol and dried to leave 45 gof octabutoxynaphthalocyanine (theory: 70%).

EXAMPLE 8

47 g (0.26 mol) of 30% strength by weight methanolic sodium methoxidesolution were added to 1 l of n-pentanol. Methanol was distilled offunder atmospheric pressure to just below the boiling point of pentanol(about 137° C.). After cooling down, 106.4 g (0.4 mol) of1,4-diethoxy-2,3-dicyanonaphthalene were added under nitrogen and thebatch was stirred under reflux for 3 h. The pentanol was distilled downto a remainder of about 50 ml under a water pump vacuum, and 1 l ofmethanol was added. After stirring at room temperature for 10 h theprecipitated product was filtered off with suction, washed with methanoland dried to leave 90.3 g of a partially transalkoxylatednaphthalocyanine (R=88% pentyl and 12% ethyl) (theory: 66%; λ_(max) :862 nm; 260 000 (in toluene)).

EXAMPLE 9

18 g (0.1 mol) of 30% strength by weight methanolic sodium methoxidesolution and 300 ml of n-hexanol were introduced as the initial charge.Methanol was distilled off under atmospheric pressure to 153° C. Aftercooling down, 11.4 g (0.01 mol) of an octaalkoxynaphthalocyanine (R=70%propyl and 30% ethyl) were added and the batch was stirred under refluxfor 4 h. Hexanol was distilled off almost to dryness under a water pumpvacuum. Then 500 ml of methanol were added. After stirring at roomtemperature for 6 h the precipitated product was filtered off withsuction, washed with methanol and dried to leave 9.4 g ofoctahexyloxynaphthalocyanine (theory: 62%; λ_(max) : 864 nm; ε: 208 000(in toluene)).

III. Metallization

EXAMPLE 10

45 g (0.035 mol) of octabutoxynaphthalocyanine were stirred for 10 hunder reflux with 7 g (0.039 mol) of copper(II) acetate monohydrate in650 ml of n-butanol. Butanol was distilled off under a water pumpvacuum, the residue was stirred up with 700 ml of petroleumether for 1h, filtered off with suction, washed with petroleum ether and dried toleave 42 g of copper octabutoxynaphthalocyanine (theory: 88%); λ_(max) :849 nm; ε: 235 000 (in toluene)).

IV. Naphthalocyanine formation and metallization in one pot

EXAMPLE 11

5.4 g (0.03 mol) of 30% strength by weight methanolic sodium methoxidesolution and 180 ml of n-butanol were introduced as the initial chargeat room temperature with stirring. Methanol was then distilled off underatmospheric pressure until the boiling point of n-butanol (117° C.) wasreached in the reaction vessel. The solution was cooled down to 60° C.and admixed with 16.1 g (0.05 mol) of1,4-dibutoxy-2,3-dicyanonaphthalene. The reaction mixture was thenrefluxed with stirring under nitrogen for 2 h, cooled down to 60° C. andadmixed at that temperature with 1.9 g (0.0094 mol) of copper(II)acetate monohydrate. After 15 h of stirring under reflux, 80% of thetotal volume of n-butanol was distilled off under reduced pressure. Theresidue was stirred with petroleum ether (180 ml) at room temperaturefor 2 h, filtered off with suction and washed with petroleum ether toleave 13.4 g of copper octabutoxynaphthalocyanine (theory: 79.3% ;λ_(max) =850 nm; ε=180 000 (in toluene)).

We claim:
 1. A process for preparing naphthalocyanines of the formula I##STR3## Me is twice hydrogen or a bivalent metal-containing radicalwith or without further ligands, andR is in each case C₁ -C₂₀ -alkyl,which may be interrupted by from 1 to 3 oxygen atoms in ether function,or C₄ -C₂₀ -alkenyl, by etherification of1,4-dihydroxy-2,3-dicyanonaphthalene and formation of the metal-freenaphthalocyanine with or without subsequent metallization, whichcomprisesa) in a first step reacting the1,4-dihydroxy-2,3-dicyanonaphthalene with an alkylating agent of theformula II

    R--X                                                       (II)

wherein X is bromine or the radical RO--SO₂ O and R is in each case asdefined above, in a molar ratio of from 1:2 to 1:3 in the presence of adiluent selected from the group consisting of N,N-dimethylformamide,N,N-diethylformamide, N-methylpyrrolidone and dimethylsulfoxide, and ofa base, pouring the reaction mixture onto water, filtering theprecipitated dicyanonaphthalene of the formula III ##STR4## where R isin each case as defined above, off with suction, and washing and dryingit, b) in a second step converting the dicyanonaphthalene of the formulaIII with an alkali metal alkoxide into the naphthalocyanine of theformula I where Me is twice hydrogen in the presence of an alcohol, themolar ratio of alkali metal alkoxide:dicyanonaphthalene III being from1:2.5 to 2.5:1, and optionally then c) in a third step converting theresulting metal-free naphthalocyanine by reaction with a metal salt inthe presence of an alcohol into the metal-containing naphthalocyanine ofthe formula I where Me is a metal-containing ligand, thenaphthalocyanine and the metal salt being reacted with each other in amolar ratio of from 1:1 to 1:10.
 2. A process as claimed in claim 1,wherein Me is twice hydrogen or copper.
 3. A process as claimed in claim1, wherein R is in each case C₂ -C₁₃ -alkyl or C₄ -C₁₁ -alkenyl.
 4. Aprocess as claimed in claim 1, wherein R is in each case C₂ -C₈ -alkyl.